The present invention disclosed herein relates to a communication system, and more particularly, to a sub-sampling receiver.
With the miniaturization trend of a wireless communication system, needs for a next-generation wireless communication receiver having flexibility, adaptability and cognitivity are increasing. In order to satisfy these needs, there is a need for a technology to design a receiver of which the analog-to-digital converter (ADC) is as similar as possible to an antenna and which performs frequency conversion and demodulation functions by using a digital signal processor (DSP). As a next-generation wireless communication receiver satisfying such a condition, a sub-sampling receiver is taking center stage. The sub-sampling receiver may provide excellent functions in aspects of the re-configurability of a received signal and multi-band/multi-mode reception.
A general sub-sampling receiver may receive an analog RF signal through an antenna and extract an analog signal in a certain band through an analog band-pass filter. An extracted analog signal in the certain band may be amplified through a low noise amplifier (LNA), and then converted into a base-band signal in digital form through an analog-digital converter (ADC). Since the sub-sampling receiver does not use an analog element such as a mixer, local oscillator, etc., it is possible to provide a wireless communication receiver that is flexible, inexpensive and small. However, a typical sub-sampling receiver has a limitation in that it is possible to down-convert a received analog RF signal into the base-band signal in digital form only when a carrier frequency becomes a multiple of a sampling rate in receiving a single RF signal.
Thus, when there is a need to receive a signal located at any frequency band by using the typical sub-sampling receiver, the sampling rate should be determined so that aliasing does not occur in a baseband after digital conversion. However, determining the sampling rate at which aliasing does not occur is very complicated and furthermore, there are many cases where there is no solution for the sampling rate at which the aliasing does not occur. Thus, there is a limitation in receiving an RF signal located at any frequency band by using the typical sub-sampling receiver.
A second-order bandpass sampling receiver suggested in order to solve these problems samples by using two ADCs and then removes aliasing by using signal processing. Thus, the sampling rate may be selected without considering the aliasing. However, since a typical second-order band-pass sampling receiver uses two ADCs, it increases hardware complexity and has a serious performance degradation resulting from an analog time error between two signal paths and imbalance in an analog signal size.